It is known that a significant amount of aerodynamic drag is created when a vehicle travels at typical velocities on a modern roadway. This is partly due to areas of low pressure that act on the rear surfaces of the vehicle. The low pressure becomes more pronounced as airflow over the vehicle separates from the vehicle surfaces. The phenomenon of airflow separation is also well known in the design of aircraft wings and, in this case, causes the wing to stall.
Vehicles with blunt rear ends are especially affected by airflow separation, often starting at the abrupt transition to the rear—near vertical surface. The low pressure that the airflow separation causes is compounded by the relatively large area that the low pressure acts over as compared with more streamlined vehicles.
The low air pressure acting on the rear surfaces of a moving vehicle produces a force that resists the forward motion of the vehicle. This force is opposed by the vehicle's engine and requires power that is typically produced by burning fuel. Any reduction in aerodynamic drag results in a reduction in fuel consumption.
In a period of high fuel prices, increasing fuel efficiency is a growing concern. Aerodynamic improvements are especially valuable since they can be combined with other improvements such as engine efficiency and reduced chassis weight. Increasing fuel efficiency also provides the valuable benefit of increasing the range a given vehicle can travel between refueling.
The present invention uses the technique of tapering the rear surfaces of a vehicle. The same technique is in use with other vehicles such as streamlined cars and airplanes. It has also been applied to over-the-road trucks where it is known as a “boat-tail”.